A color model is an abstract mathematical model describing the way colors can be represented as tuples of numbers (e.g. three-tuples in sRGB and four-tuples in CMYK). The provision of a specific mapping function between a color model and a reference color space establishes a specific “footprint” within the color space referred to as a gamut. Thus, a gamut indicates the envelope, or volume of color, a specific device can render in a color space. When defining a color space, a usual reference standard is the CIEXYZ color space, which represents the spectral responses of the human eye, or the CIELAB color space, where equal distances in the space corresponds (very roughly) to equal perceptual color differences (a “perceptually uniform” color space). Referring to FIG. 1, there is shown the wide gamut RGB color space 100, the sRGB color space 105, the CMYK color space 110, and the D93, D65 and D50 white points 115 relative to the visible color spectrum 120 in the CIE xy chromaticity diagram.
In digital imaging applications, there is often a need to efficiently estimate an image's color gamut boundary, i.e. the smallest gamut size needed to render all colors in the image with good visual accuracy. A gamut size metric could provide a way to determine if a wider gamut is needed to represent a particular image, and if so how wide it needs to be. Such a metric has applications at all stages of color imaging processing.